Your hormones could still be out of whack. Babies, especially girls, drain your body of all the good stuff. I had my son first, not so bad, but then when I had my daughter, hair loss, cavities, you name it I had it. It also has been very hot and humid over the past few weeks which drains energy from you. Just going in and out of air conditioned places will cause your body to work over time. I did a run yesterday that was a minute/km slower than my usual time? You don't sleep the same after having kids either, I don't anyway.
I think as long as you keep at it, you won't loose it. A good jogging stroller would be useful. My schedule changes in the summer because my kids aren't in school and it is harder to get out on the streets. This is my first summer that I'm keeping up with my running. I used to take the summers off ( only running on weekends and holidays) and I was still doing half marathons in the spring.
Keep at it, as long as you have the drive to do it, you will get it done. It will be frustrating until you find a schedule that fits your new lifestyle. And it will start to cool off soon...
Good luck
